Air pressure operated gun



United States Patent Inventors AIR PRESSURE OPERATED GUN 17 Claims, 8 Drawing Figs.

US. Cl

Int. Cl

Field of Search 124/11, 12fi/3l,124/41,73/l2 ..F4lb 11/00,

31, 4l;'73/l2(Whalen), 167(Prince), 40.5; 89/1 .801

i [56] References Cited UNITED STATES PATENTS 1 3,167,061 l/1965 Murray l24/ll i 3,422,808 l/l969 Stein et a].

Primary Examiner-George J. Marlo Assistant Examiner-William R. Browne Att0rneyLawrence E. Laubscher ABSTRACT: A gun for the discharge of projectiles comprises a barrel initially closed at each end by a disruptable closure. and containing a projectile adjacent one end. Air is evacuated from the barrel and the closure adjacent the projectile is disrupted so that the projectile is accelerated down the barrel I by the inrushing atmospheric air to disrupt the other closure and be discharged from the gun. The projectile may be carried in a sabot and may be connected by a wire initially coiled within the gun barrel to a recorder, or a radio link may be used. The discharged projectile may be arrested by firing it into a receiver tube aligned with the barrel to compress the air i therein.

Patented Oct. 27, 1970 Sheet 1 of 2 4 R I I O M, at 0% I w H o O .3 & N3 W mm M W mm NW .m i I R omm 9 m? k n fig Us 2 mv W m Q a /J r j A X 1 m mm,

mm NMlI/ mm. ,9 W /4 F/ Mm 0 Q U 0Q Q m mm a.

X Ml/L ATTORNEY Patented Oct. 27, 1970 Sheet R I 7% 2&7 Q? Q k c. J ww Q mm mm mw gfim t @Ewa Q: ma a m Vwt n 9k A r/ R a a 4/ Q \Q Q N @V Q E Q i a Q R mm g 02 ATTORNEY AIR PRESSURE OPERATED GUN INTRODUCTION This invention relates to guns. More particularly, this invention relates to a gun which is suitable for use in a variety of tests, such as impact tests in which a projectile is fired into a target, free flight tests in which a projectile is fired into free flight, and acceleration tests in which an article is subjected to a relatively prolonged acceleration.

It is an object of the invention to provide a gun for discharging a projectile which avoids the use of combustible material.

It is a further object of the invention to provide a gun for discharging a projectile which does not employ gas pressures increased above atmospheric pressure.

It is another object of the invention to provide a gun producing a minimal disturbance of the air at the point of discharge of the projectile.

It is an additional object of the invention to provide a gun such that a discharged projectile may readily be arrested without damage.

Features and advantages of the invention will appear from the following description of an embodiment thereof, given by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic sectional view of a gun in accordance with the invention;

FIG. 2 is a partial plan of the gun of FIG. 1;

FIG. 3 is a sectional end elevation taken along the line 33 of FIG. 1;

FIG. 4 is a partial sectional elevation illustrating a modification of the gun shown in FIG. 1;

FIG. 5 is a diagram illustrating one use of the gun;

FIG. 6 is a diagram showing a projectile disposed in a sabot in the breech of the gun, ready for firing;

FIG. 7 is a diagram showing another projectile; and

FIG. 8 is a diagram illustrating a magnetic tape-recorder device which may be used in a projectile.

The gun shown in FIG. 1 is operated by vacuum. The gun comprises a barrel which may be connected to a vacuum pump, the muzzle and breech of the barrel being sealed by diaphragms. In use, the projectile is placed in the breech, and the muzzle and breech are sealed by the diaphragms. The barrel is then evacuated. The breech diaphragm is then punctured and air flows in from the atmosphere. This applies a pressure to the base of the projectile, which is thus accelerated down the barrel to puncture the muzzle diaphragm and emerge from the barrel. If the projectile does not conform to the cross section of the barrel it may be placed in a sabot, and it may be desired to separate the sabot from the projectile after firing. Separation is partly achieved by the aerodynamic pressure on the sabot as it emerges with the projectile from the muzzle, but a baffle may also be provided to catch the sabot, while permitting the projectile to continue.

The gun is particularly simple in construction and operation, but its operation is accurately reproducible. High muzzle velocities can readily be achieved without applying explosive accelerations to the projectile.

One particular advantage of the gun is that there is little ly, the projectile can be fired into a yielding target to give a prolonged deceleration which can be a predetermined function of time.

Referring now to FIGS. 1, 2 and 3 the gun comprises a barrel 10 which may conveniently be made of a resin-bonded paper material, although fibre glass or metal barrels are also disturbance of the air at the muzzle end of the gun caused by the propellant, since the propellant is air at atmospheric pressure.

Accordingly, the gun finds a particular use where it is desired to make impact tests on a liquid, since the muzzle of the gun can be placed quite close to the liquid target, without disturbing the surface of the liquid before the arrival of the projectile.

Another particular use of the gun is in acceleration tests, since the acceleration of the projectile along the barrel is relatively prolonged and for some experiments can be treated as approximately constant. Accelerations several hundred times the acceleration due to gravity, that is to say, of several hundred thousand centimetres per second can readily be achieved for periods up to and exceeding l00milliseconds. Alternativesatisfactory in some circumstances. The barrel 10 is provided with a flange 11 at the breech end, and a similar flange 12 at the muzzle end, these flanges being provided with annular grooves 13, 14 containing O-ring seals 13a and 14a. A pipe union 15 is provided by which the interior of the barrel can be connected by way of a conduit 49 to a vacuum pump 50. An annular clamp member 16 is provided at the muzzle end of the barrel, for clamping against the O-ring seal a circular diaphragm 17 of thin and flexible sheet material, such as Melinex, which may have a thickness of 0.002 inches. The diaphragm I7 is sufficiently strong to withstand atmospheric pressure when the barrel is evacuated, but equally is sufficiently weak to burst readily on impact of the projector when the gun is fired. A similar diaphragm l8 and clamping member 19 is provided at the breech of the gun. The clamping members l6 and 19 may be tightened on to the barrel by pins such as 16a, which are urged against the clamping ring by hydraulic pressure, applied by hydraulic cylinders such as 16b, so as to obtain a reproducible pressure on the O-ring seals 13 and 14. Alternatively, the clamp members 16 and 19 may be arranged to be clamped by screw clamps such as 16c or to screw on to the muzzle and breech as shown in FIG. 4, where it will be seen that clamp members. 16 and 19 are provided with annular, internally screw-threaded flanges 16a, 19a which engage with external screw threads formed on barrel flanges l2 and II respectively.

The clamping member 19 is provided with a collar 20 which supports the breech mechanism. The breech mechanism is arranged to puncture the breech diaphragm 18 when a gun is to be fired. In the embodiment shown in Fig. l, the breech mechanism comprises a ring 21 carrying at its periphery a ring of blades 22. The ring 21 is provided with a plurality of guide pins such as 23, which cooperate with inclined slots such as 24 formed in the collar 20 to guide the movement of the ring 21. The serrated edges of the blade 22 are inclined in the opposite sense to the slot 24. A solenoid actuator 25 (FIG. 3),is provided which is mechanically coupled to ring 21 by means of a link 25a so that when the solenoid is energized, ring 21 is sharply rotated, so as to drive the blades 22 into the diaphragm 18 at the periphery of the bore of the barrel 10. The entire diaphragm is thus cut out sharply and quickly, permitting air to flow smoothly into the evacuated barrel 10.

In the embodiment shown in FIG. I the projectile 26 which is to be fired is smaller than the bore of the barrel l0, and is supported in a sabot indicated at 27. The sabot acts as a piston of which the head is a close fit in the bore of the barrel l0, and which has an annular skirt 28 projecting forwardly from the head of the sabot, the forward end of the skirt being sharpened, so as to sever the diaphragm 17 at its edge. The sabot 27 is conveniently made from a low density material such as expanded polyurethane, although other expanded plastics materials, or wooden materials, could be used. The expanded polyurethane is formed with a tough skin at its surface, which gives the body sufficient structural rigidity. However, the material is not sufficiently strong to transmit the acceleration force to the projectile directly, and a rigid load distributing plate 29 is positioned behind the projectile 26 and the inner surface of the base of the sabot. Radial supports 30 and 31 are provided to hold the projectile against lateral movement.

To separate the material of the sabot 27 from the projectile 26 when the gun is fired, a separator 32 is preferably provided outside the muzzle of the gun. This separator comprises a baffle plate 33, having an aperture 34 coaxial with the barrel 10. A tube 35 is mounted on the muzzle side of the baffle 33. When the projectile and sabot emerge from the muzzle of the gun, the sabot is usually retarded by the air pressure more rapidly than is the projectile, and separation begins. In any case, the projectile 26 passes into and through the tube 35, while the skirt 28 of the sabot passes outside the tube. The projectile is thus free to carry on unimpeded, while the skirt 28 disintegrates against the bafile 33, and the plate 29 and base of the sabot are stopped by the tube 35. A certain amount of material from the sabot may pass down the inside of the tube 35, but this will usually have been delayed considerably by the acerodynamic pressure, and by the disintegration of the sabot, and will follow same distance after the projectile.

The speed of the projectile may be measured by measuring the time taken for the projectile to traverse a known distance. For instance, pulses may be generated by the projectile breaking two wires in succession, which are separated by a known distance in the direction of motion of the projectile. In .a preferred method, two members of soft iron material are secured to the projectile spaced apart in the direction of its motion, and the passage of these two members is sensed by a stationary magnetic pickup, which may for instance comprise a magnetic circuit energised by a coil, and including an air gap disposed beside the path of movement of the two soft iron members. The two electrical pulses derived may be displayed on an oscilloscope, so that the spacing of the pulses as seen on the cathode ray tube of the oscilloscope is a measure of the velocity of the projectile. Alternatively, the two pulses may be used to start and stop a counter fed with clock pulses recurrent at a known rate.

When acceleration tests are to be conducted, it is often desirable not to destroy or mutiliate the projectile fired. To prevent this, the projectile may be fired into a mass of soft material, such as cotton waste. Preferably, however, as shown in FIG. 5, the projectile is fired into a tube 36 which is closed at one end, and which contains air at atmospheric pressure. As the projectile enters the tube 36, it compresses the air in the tube in front of it, and a relatively gradual deceleration is applied to the projectile. To prevent the projectile from being returned back down the tube 36 by the airpressure built up in the tube, a restricted outlet 37 is provided from the closed end of the tube 36. if the projectile is mounted in a sabot, it is necessary to secure the projectile very securely to the sabot, and the sabot must be made sufficiently strong to withstand the sudden reversal of acceleration. The sabot 27 described in relation to FIG. 1 would not be suitable. Alternatively tube 36 could be made with an internal diameter suited to that of the projectile.

The dimensions of the projectile or sabot are fairly critical. However, a certain amount of clearance of the projectile from the bore of the barrel can readily be tolerated, and in fact a clearance of about one tenth of an inch is preferred for a sabot with a diameter of 10 inches. In this connection, leakage of a small amount of air round the side of the projectile may act to lubricate the motion of the projectile. In a typical case, the length of the barrel 10 was ft., its diameter was l0.2 inches, the projectile mounted in the sabot 27 weighed 3 lbs., and the barrel 10 was evacuated to approximately one tenth millimetre of mercury. The acceleration achieved was approximately 400 times the acceleration due to gravity, and the muzzle velocity was approximately 600 ft. per second.

It is possible to vary the acceleration and muzzle velocity by varying the weight of the projectile, by varying the initial position of the projectile in the barrel 10, by varying the length or diameter of the barrel 10, or by varying the pressure of air remaining in the barrel 10 before firing. This last method may not be desirable, since retardation of the sabot may occur before the diaphragm bursts, and the projectile may be projected through the diaphragm ahead of the sabot.

It is often required to record signals generated within the projectile in motion, such signals for instance being indicative of the time of occurrence of an event, such as the time relative to first touch when an impact device has effectively operated. The signals may be transmitted to a stationary recorder either by means of a trailing wire, or by a radio link. FIG. 6 shows an example of the way in which a trailing wire system can be arranged in a gun according to the invention. Before the gun is fired, a coil 38 of light flexible wire, preferably a coaxial cable, is positioned in the breech of the gun behind the sabot 27, the stationary end 38a of the cable passing out through the side of the gun barrel to a suitable recorder 51. The cable extends into the sabot, and a further small coil 39 is formed in the sabot behind the projectile. The inner end of the cable is secured to the projectile, and is connected to the relevant device under test. The total length of cable in the coils 38 and 39 must be greater than the total distance to be travelled by the-projectile.

As the projectile accelerates down the gun barrel, the cable is pulled after it, and this sets a limit to the length of gun barrel with which the trailing wire method can be employed. The acceleration of the length of cable to follow the projectile 26 down the gun barrel puts the cable under a heavy tension, and the longer and heavier the cable is, the greater is this tension. For this, and other reasons, it is sometimes preferred, as shown in FIG. 7, to use a radio link between the device in the projectile and a stationary recorder. The projectile then includes a small frequency modulation transmitter, coupled to an aerial 40 which conveniently projects out of the back of the projectile. Signals transmitted from the projectile may be picked up by an appropriately positioned aerial but, particularly where the projectile is fired at a target which reflects radio waves, the limited response of the receiver should be fast-acting, since rapid signal level fluctuations occur due to the movement of the projectile, and of its radio image reflected in the target. The transmitter in the projectile is conveniently a thin film construction encapsulated in a moulded plastics material, so that the transmitter can survive the high acceleration stresses imposed in use.

Alternatively, instead of transmitting the information to a stationary recorder, a miniature tape recorder may be incorporated in the projectile. H6. 8 illustrates such a device. in this device, a moulded plastics base member 41 is provided with a pair of cavities 42 and 43 which receive and closely support a pair of spools 42a, 43a carrying a length of magnetic tape. Two magnetic recording heads 44 and 45 are provided beside the tape path, to provide four-track recording on the magnetic tape. The tape is driven past the spools by a simple spring drive whose release is controlled by a star and pallet device, the drive being applied to the spindle of one of the tape spools. Where it is required to record the relative times of occurrence of one or more events, a simple plastics encapsu-' lated oscillator can generate a reference frequency signal, which is switched on and off in response to the events to be recorded. Although the movement of the tape is not exactly uniform, or exactly known, the number of cycles of the reference signal recorded during the time which is to be measured can be counted to give an accurate measure of the time. The tape recorder is virtually destroyed after one impact, but the nature of the base member 41 which closely supports the tape prevents the tape itself from being destroyed, and the simple construction of the device makes it readily expendible. It will be apparent that this tape recorder device also has a number of applications apart from its use in conjunction with the vacuum gun.

H68. 6 and 7 show a suitable design for the projectile for an impact test, in which the device to be tested is shown at 46, being supported from the main body 47 of the projectile by a frangible structure 48. Ancillary equipment, such as the transmitter of the device of FIG. 7 is mounted in the main body 47 of the projectile, so as to continue operating while the device 46 strikes the target. The structure 48 collapses when the device 46 strikes the target, so that it is only subsequently that a substantial impact. force is applied to the main body of the projectile 47.

Where it is desired to measure the time of operation of an impact device relative to the first touch of the projectile, the

be applied by an electrode immersed near the target point); when the projectile touches the target, a high voltage pulse is applied to the earth wire of the cable, which can be used to mark the time of first touch. This method is not available where the radio telemetry method of FIG. 7 is used, but the first touch can be calculated by the distance seen on a photograph which is triggered by the projectile breaking an electric circuit before first touch.

Again, the time between the two events, such as between first touch and operation of the impact device may be measured by starting and stopping a counter to which clock pulses are applied, or by applying the pulses to an oscilloscope and measuring the spacing of the pulses on the cathode ray tube.

We claim:

1. A gun, comprising:

tubular barrel means having open ends;

first and second closure means positioned at opposite ends of said barrel, respectively;

closure fastening means securing each said closure means to the respective ends of said barrel;

evacuating means operable to withdraw air from said barrel between said first and second closure means;

a projectile;

projectile support means supporting said projectile and fitting slidably within said barrel, said projectile support means being positioned adjacent the first one of said closure means; and

closure disrupting means including annular blade means axially displaceable of said barrel for disrupting said first closure means, whereby said projectile and said projectile support means are accelerated towards, and discharged from said barrel through, the second one of said closure means by the force of atmospheric air entering into said barrel through said disrupted first closure means.

2. The invention defined in claim 1, wherein said first disruptable closure means comprises a thin membrane of synthetic plastic material.

3. The invention claimed in claim 2, wherein said closure fastening means comprises a radially outwardly directed flange extending around the periphery of said barrel at an end thereof; clamping means clamping said membrane to said flange; and sealing means sealing said membrane to said flange in an airtight manner.

4. The invention claimed in claim 3, wherein said flange contains an annular groove in the face thereof engaged by said membrane and a resilient O-ring positoned in said groove to provide said seal.

5. The invention claimed in claim 2, wherein said fastening means comprises an annular ring having a radial face; a flange on said barrel, a clamping device operable to urge said ring towards said flange thereby clamping said membrane between said flange and said clamping device.

6. The invention claimed in claim 5, wherein said clamping device comprises a screw clamp operable to urge said ring and said flange together.

7. The invention claimed in claim 5, wherein said clamping device comprises hydraulic means for urging said ring and said flange together.

8. The invention claimed in claim 5, wherein said clamping device further comprises an external screw thread formed on the radially outer surface of said flange, an axially extending collar formed on said ring, an internal screw thread on said collar mateable with said external screw thread, whereby said ring and flange may be screwed together.

9. The invention claimed in claim 5, wherein said closure disrupting means comprises an annular collar means extending axially from said annular ring and having a plurality of helical slots formed therein; ring means rotatably and slidably mounted in said collar means; a plurality of pin means each fixed to said ring means and each engaged in a respective one of said helical slots whereby rotational movement of said ring means produces axial movement of said collar; an annular array of knife blades; means mounting said array of blades on said ring means for engagement with an annular zone of said membrane in response to axial inward movement of said ring means; and actuator means coupled with said ring means to produce said rotational movement thereof.

10. The invention claimed in claim 2, wherein said closure disrupting means comprises a blade means; means mounting said blade means for movement between a first position remote from said membrane and a second position penetrating said membrane, and drive means operable to cause said blade means to move from said first to said second position.

11. The invention claimed in claim 1, wherein said projectile support means comprises a sabot of lightweight material fitting slidably within said barrel, said sabot having an annular skirt portion forming a recess for said projectile; a projectile pressure distributing plate in said recess; a projectile in said recess abutting said pressure distributing plate; said projectile support means comprising means for centering said projectile in said recess.

12. The invention defined in claim 11, and further including a projectile and projectile support separator means positioned adjacent the end of said barrel from which said projectile lS discharged, said separator means comprising a projectile support impact baffle plate means containing an aperture at least the size of the projectile and aligned with said barrel; and tube means extending from said plate means towards said barrel around said aperture.

13. The invention claimed in claim 1, and further including elongate electrical conductor means connecting signal generating means in said projectile with stationary recorder means.

14. The invention defined in claim I, and further including radio transmitter means contained in said projectile.

15. The invention as defined in claim 1, and further including signal generating means and signal recorder means contained in said projectile.

16. The invention recited in claim 1, and further including projectile arresting means comprising receiving tube means aligned with said barrel means for slidably receiving said projectile, said tube means having an open end directed towards said barrel means and having a closed end remote therefrom 17. The invention defined in claim 1, and further including projectile arresting means, comprising tube means slidably receiving said projectile, said tube means having a closed and an open end; and means mounting said tube means in alignment with said barrel means to receive a projectile discharged therefrom. 

